This invention relates to the focusing of high energy laser beams. In particular, it relates to the alignment and focusing of high energy laser beams wherein the frequency of the laser is converted by passing through a conversion crystal before impacting on a target. The system utilizes a single low intensity laser beam which is not affected by the crystal, for the alignment and focusing.
Presently, most large multi-amplifier laser devices utilize two separate, low intensity laser beams to align the main laser: one to align the beam through the laser and the other to align the beam from the conversion crystals to the target. In utilizing this system it is necessary to align the two laser beams one with the other and then subsequently compare the alignment on the target to the resulting high energy beam. The reason two separate alignment lasers have been used rather than one, is because of lens dispersion of the different frequency light after the beam passes through the conversion crystal. In short, the main beams, because of their high energy are often converted to a higher frequency before hitting a target. This conversion occurs with a high intensity beam. Since the alignment laser beam is of low intensity, it does not convert as it is passed through the conversion crystal. After the high intensity beam is converted to a higher frequency, it passes through a lens which focuses the beam onto a target. Because of the dispersion characteristics of a lens, the focal point for the higher frequency beam will be closer to the lens than the low intensity beam which does not convert. For example, a laser beam of low intensity and of a particular frequency and a wave length of 1054 nm will be unaffected by the conversion crystal. If that same 1054 nm laser is raised to a high intensity, when it passes through the conversion crystal in the laser it exits the conversion crystal with the higher frequency and a wave length of 351 nm. The 351 nm laser beam, as noted above, will focus closer to the focusing lens than the low intensity beam of 1054 nm. To provide an alignment beam which focuses on the target as in the main beam, in the past, a second alignment laser beam was injected into the system which had the same frequency as the main beam after conversion, i.e., 351 nm wave length in our example. As also noted, this requires co-alignment of the two alignment laser beams, i.e., the co-alignment of the 1054 nm and 351 nm beams in our example.
If it were possible to use a single alignment beam for both laser and target alignment, then there would be no need for a second alignment laser nor the need to co-align the two separate alignment laser beams.
This invention describes a device that permits one to use a single and low intensity alignment laser for both laser and target alignment, wherein the device compensates the low intensity alignment laser beam to focus and point a the high intensity beam in spite of the frequency dispersion caused by the focusing lens.
A second function of the present invention is to align a target relative to the laser beams once the above beam alignments have been accomplished.
The second function is currently performed by indirect viewing devices that are located near the target's final position. These indirect viewing devices may also be inaccurate and costly.
It is a object of this invention to provide a low cost means for compensating, sensing and imaging laser beams to a very high focus and a very high pointing accuracy.
It is also an object of this invention to position a machine tool adjacent to a workpiece with a great degree of accuracy.
It is a further object of this invention to provide means to focus coaxial laser beams having different frequencies.